This is currently an incomplete work in progress!! Please
expect it to change
Guide to Testing a Kernel
EWS Disk Space Quotas
Each student on EWS is allocated 3Gb of disk space for their overall
work. Unfortunately, in this course you will need a fair piece of
that. Please take some time at the start of this semester to clean up
your directory to avoid difficult situations later on.
If you should ever find yourself having exceeded your quote, you may
have trouble even removing files. In this case, you should try
executing:
cat /dev/null > <some_big_file>
If all else fails, you might try moving a file
temporarily to /scratch, which is local
storage on the server itself. This is a shared resource, so you must
make sure to monitor this disk usage carefully, and be sure to remove
any files afterwards.
Using the QEMU Environment
This semester, we are using the QEMU machine emulator.
One advantage of QEMU is its ability to run a linux kernel image that
was compiled outside the Virtual Machine. We will be compiling the
kernel directly on the EWS machines, instead of inside a virtual
machine running in qemu (running on an EWS machine).
This will save us a fair bit of time. However, the price we pay for
this will be more complicated start-up procedure, as you will see
below.
QEMU has been installed on the EWS Linux machines for us to use. When
running qemu, or any of the related programs, please
run it from a window that is dedicated to that, that you would not mind
killing, and do not run qemu in the background. If
something goes wrong you want to be able to kill qemu and
killing the window that spawned it will do this (particularly if it is
not running in the background).
To start up qemu with a small linux kernel (version
2.6.20), execute
qemu-system-x86_64 -hda ~cs423/disk_images/linux-0.2.img -no-reboot -curses
If you are running X11 and and connected with the -X or
-Y flag, and you are not using a Mac, you may be able to
leave off the -curses and have qemu run in a
separate window. If you are running on a Mac, you might want a liitl
extra protection form system lockup given by running xterm -font
10x20 from within the xterm you used to
ssh to remlnx.ews.illinois.edu.
The -hda option specifies a disk image from which to
boot. The -no-kqemu option specifies not to use
kqemu, which has not been installed on the EWS machines.
The -no-reboot option specifies not to automatically
reboot the VM when we exit.
If this much is working, you should find yourself in a shell. You can
do some basic things like ls and cd.
Creating a COW Disk Image
At this point, you need to have a disk image of you own to modify and
use. There is a base Ubuntu image (without a bootloader) found in the
same disk_images directory as
linux-0.2.img. However, this image exceeds 3G in size,
and would likely blow away your quota if you were to try to copy it.
Still, this is the base from which you will need to work for testing
the kernels you will build in some of the mps. The solution for htis
is to make a COW (copy-on-write) disk image as follows:
qemu-img create -b ~cs423/disk_images/ubuntu_noboot.img -f qcow2 <your_mp_dir>/mp1.img
The base image ubuntu_noboot.img does not have a
bootloder installed. Therefore, it can't be used in quite the same
way as linux-0.2.img above. Instead we will boot using
an additional -kernel option that allows us to supply
externally a kernal from which to boot.
Cofiguring the Kernel
We will be using Linux kernel
version 2.6.37.0 this semester. You should begin by creating a
directory <your_src_dir> into which you will
put the source for the linux kernel. Having created that, next you
need to populate it. We have put a bz2 compressed copy
of the source for linux-2.6.37.0 on the ews machines. To
use it to populate <your_src_dir>, execute the following:
tar -xjf
~cs423/semesters/curSemester/resources/linux-2.6.37.tar.bz2 -C
<your_src_dir>
The next
step is to configure your your kernel. Change into
<your_src_dir> and run
make menucofig
To enable networking, in the menu that comes up, go to
Device Drivers --> Network device support --> Ethernet (10 or
100Mbit)
and change "PCI NE2000 and clones support" to
be compiled into the kernel (as opposed to being a module). The
network driver will be crucial for us to install all the other
modules. Exit and save. If you do n;t wish to include networking at
this time, you may just exit and save without making any changes.
Compiling a Kernel Image
Once you have finished configuring the kernel, you can compile the
kernel by executing (in the same directory) the following:
make -j16 bzImage
This will create a file
<your_src_dir>/arch/x86_64/boot/bzImage
Booting QEMU with an External Kernel
Once you have created a custom kernel, you may start up
qemu with this kernel by executing
qemu-system-x86_64 -hda <your_mp_dir>/mp1.img
-kernel <your_src_dir>/arch/x86_64/boot/bzImage
-append "root=/dev/hda1" -m 1024 -no-reboot -curses -net nic,model="ne2k_pci" -net user
This will boot the custom kernel image, with root filesystem
/dev/hda1 and 1024M (1G) of RAM. The boot should be
successful, however you will see error messages on boot, such as
modprobe: FATAL: could not load /lib/modules/2.6.28.37/modules.dep: No
such file or directory
This is because although we are booting the custom kernel image, we do
not have the modules installed.
To check out that all is working, you may log in to the machine as
cs423 with password cs423. To confirm that
you are running the kernel you just compiled, run
uname -a
You should see 2.6.37.0. Or get more detailed information using
dmesg. One of the first few lines should have output
similar to
Linux version 2.6.37 (egunter@linux2.ews.illinois.edu) (gcc version
4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Mon Jan 24 21:45:40 CST 2001
To exit qemu you may execute
sudo halt -p
and give cs423 as the password when requested.
Last modified: Thu Jan 27 22:37:42 CST 2011